Multiplexing LED Drive and a 4x4 Keypad

Posted on Jun 19, 2012

Typically applications having LEDs and keypads also keep track of real-time, in order to synchronize certain related events. An Industrial Clock/Timer example has been used in this application note as a demonstration of these functions. The software overhead to keep track of real time is minimal and the user can modify the code to significantly expand the functionality of this circuit.

The 4x4 Key Matrix is connected to PORTC of the PIC16C5X (Figure 2). The four columns are connected to RC0-RC3 and the four rows are connected to RC4- RC7. Each digit is refreshed every 20 ms. with a 5 ms pulse. The keypad is sampled every 20 ms with

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